It seems the first question every man who is involved with a T-Girl gets is “Are you Gay?” Trans-phobia and misplaced homophobia and all of the dangers and epithets associated with them are a very real possibility for the trans couple, as is (depending on locale) straight-up discrimination in public accommodation such as hotels, restaurants, hospitals or even bathroom usage.
If you’re lucky enough to live in a large city in North America or Europe, there’s likely laws on the books that protect the rights of the trans-gendered, though threats to one’s safety can happen anywhere. It is common knowledge that there are individuals who cannot tolerate differences in others. These bullies can be motivated by any of a number of issues including trans misconceptions, though it being their issues, best not concern yourself with them. Depending on your assessment of the situation at hand, a verbal confrontation explaining that their actions will not be tolerated may be in order, or perhaps it would be best to ignore them, in any case it’s not worth risking your or your partner’s lives.
Particularly if your transgendered girlfriend is not particularly feminine, and cannot “pass” for whatever reason, it may be best to avoid settings and situations where harassment is likely to occur. In larger communities there are transgendered venues that cater to the trans community, in smaller ones gay-friendly bars and restaurants will likely provide a more inviting atmosphere than say, a red-neck sports bar. As always, common sense should prevail.